Wednesday 3 September 2008 09.02 EDT
First published on Wednesday 3 September 2008 09.02 EDT

Barack Obama has reached the 50% mark in polling of US voting intentions, giving him a clear lead in the race for the presidency.

A well-received acceptance speech at the Democratic convention in Denver last week, coupled with the fallout from John McCain's choice of Sarah Palin as running mate, helped Obama gain five percentage points in yesterday's Gallup tracking poll.

Up to this point, no more than 49% of registered voters had supported Obama for president, according to the daily tracking. McCain's figure of 42% yesterday was well below his peak of 48%.

McCain will hope to turn things around today as the Republican convention gains pace after the early part of the programme was disrupted by hurricane Gustav. Palin is due to address the delegates tonight.

Reaching 50% is a symbolic milestone, but the poll gap between Obama and McCain was not the widest of the campaign. When he returned from his trip to Europe and the Middle East in July, the Democratic candidate was nine percentage points ahead of his rival, at 49% to 40%.

The proportion of undecided voters in the latest poll was 8%, slightly lower than in August, when the figure hovered at 9-11%.

Daily tracking polls are not considered as reliable as regular polls but give a useful gauge of what has transpired in the past fortnight.